The junior detective genre is attractive to writers because its conventional tropes – withheld information, mysterious motives, false identities, red herrings – mirror adolescent experience in the baffling, adult-controlled world. It also suggests that things will, in the end, make sense; and insists that being a child is no barrier to bringing about justice. It is, therefore, a mendacious genre.

In Nina Bawden's Carrie's War, wise young Albert complains: "It's a fearful handicap being a child. You have to stand there and watch, you can never make things happen. Or stop things you don't like." This is an inconvenient truth for writers of crime thrillers with an adolescent hero. One way round it is to feature young protagonists, such as Horowitz's Alex Rider or Higson's young Bond, who are not subject to the normal constraints – to make the crime thriller a sub-species of fantasy.

Kevin Brooks, a writer not averse to taking risks, chooses the road less travelled. In The Ultimate Truth he attempts to write a young private eye story that is both plausible and set in real place and time. Does he succeed? Yes, and brilliantly. Disbelief is left suspended by a single thread, but it holds. (In fact, one of the many pleasures in reading this novel is wondering whether both Brooks and his young hero will get away with it.)

Travis Delaney, 13, becomes a private investigator because he was born to it. His parents were gumshoes, Delaney & Co, a firm founded by his grandfather, now retired. "Were", because they are dead, killed in an inexplicable car crash before the novel opens. The first chapter shows us their funeral. As much to staunch his grief as anything else, Travis looks into the case his parents were investigating at the time of their deaths: the disappearance of a promising young boxer, Bashir Kamal. In so doing, he kicks a hornet's nest; soon the town is buzzing with spies.

This is not a simple read – the Northern Irish Troubles, jihad and inter-agency rivalries among the Intelligence Services all feature – but it grips. You really do want to know what happens next, as does Travis. Brooks declines the Young Sherlock option: much of the time, Travis has no idea what is going on. A surfeit of information hurts his head. He's out of his depth. He's only 13, after all. And bravely, ironically, Brooks betrays his book's title; we do not arrive at the ultimate truth. The denouement is anticlimactic in that no one is brought to justice. The baddies – or are they goodies, or neither? – melt away, leaving Travis and his grandad somewhat wiser and more resolute.

Brooks's novels for older readers often centre on loss, and suggest that dealing with it is a matter of acceptance and stoicism. Thirteen is a little young for stoicism, and Travis is dependent upon the support of his family and his friends. So, as well as being fast-paced, sharp and absorbing, The Ultimate Truth is, at another level, honest.

This is the first novel in a projected series. Uncharacteristically, I'm glad of it. Travis Delaney deserves a large and appreciative following among young readers who are sceptical about the unfettered derring-do of adolescent superheroes.